1. Field of the Invention
The present invention relates to an examination method of buffer capacity of saliva and an examination instrument of buffer capacity of saliva, by which the buffer capacity of saliva of a subject can be examined simply without being influenced by an amount of saliva and preciously without being influenced by the subjectivity of an examiner.
2. Description of the Conventional Art
The forming and progress of dental caries are made in the following steps. That is, when demineralization wherein acids produced by the metabolism of hydrocarbons by bacteria in an oral cavity elute calcium ions and phosphate ions in teeth, and remineralization that is a phenomenon wherein the calcium ions and phosphate ions are again taken into the teeth, repeatedly function over a long period of time, a balance between the both is broken, and the environment is inclined to the demineralization side for a long time, whereby the dental caries is formed and proceeds. The role of saliva includes not only a function to supply calcium ions and phosphate ions present in saliva to teeth but also a buffer capacity to neutralize acids produced by the metabolism of hydrocarbons by bacteria in an oral cavity, thereby preventing demineralization. Since there are observed differences in the buffer capacity of saliva against the acids individually, for making a guide for stopping the forming and progress of the dental caries, it is necessary to obtain objective information individually regarding the buffer capacity of saliva.
The buffer capacity of saliva is regulated mainly by the following three buffer functions: a function by the correlation between carbonic acid and a bicarbonate, a function by phosphates, and a function by proteins. Of these, the function by the correlation between carbonic acid and a bicarbonate is the most important, which is based on an equilibrium relation between carbonic acid and the bicarbonate. When an acid is added, the bicarbonate releases carbonic acid as a weak acid. This carbonic acid is rapidly decomposed into water and carbon dioxide, and then is liberated from the solution. In contrast to many buffering agents, this mechanism results in not accumulation of a weak acid but complete elimination of the acid. That is, in order that the buffer capacity of saliva based on the equilibrium relation between carbonic acid and the bicarbonate is maintained, it is considered that a sufficient amount of the bicarbonate for eliminating a large amount of the acid is needed. Further, it is already confirmed that the variation of the bicarbonate in saliva appears in a pH change.
Accordingly, for examining the buffer capacity of saliva, the evaluation of the amount of the bicarbonate through titration using an acid is the most confident, and its standard method at a laboratory level is the Ericsson method (see Ericsson Y.; xe2x80x9cClinical investigations of the salivary buffering actionxe2x80x9d, Acta. Odontol. Scand., 17:311-65 (1959)). This Ericsson method is a method in which a certain amount of hydrochloric acid is added to collected saliva, the mixture is stirred for a certain period of time while subjecting to a treatment for avoiding bubbling and inclusion of carbon dioxide, and then, the ultimate pH is measured using electrodes. However, since this method requires a complicated operation and a specific device, it is not generally diffused.
Thus, as a method for examining the buffer capacity of saliva more simply, employed is a method in which saliva is dropped to a paper having been previously immersed with a weak acid and a pH indicator and dried using a dropping pipette such that the saliva covers the whole of the paper; and after the lapse of five minutes, the pH that has increased by the saliva is determined by comparing a color of the portion to which the saliva has been added dropped with a color sample at a known pH, whereby the buffer capacity of saliva is examined according to the three grades (low, medium and high) (see Takashi KUMAGAYA, et al., Clinical Cardiology, 130-31, published by Ishiyaku Publishers, Inc.). According to this method, though it is possible to examine the buffer capacity of saliva simply, there was involved a problem that a dispersion in the amount of the saliva to be dropped, or a variation in the color determination by an examiner, is large so that errors are likely caused.
The present invention is aimed to overcome the above-described problems of the conventional art techniques and to provide an examination method of buffer capacity of saliva and an examination instrument of buffer capacity of saliva, by which the buffer capacity of saliva of a subject can be examined simply without being influenced by an amount of saliva and preciously without being influenced by the subjectivity of an examiner.
In order to achieve the above-described aim, we, the present inventors made extensive and intensive investigations. As a result, they have found the following matters. That is, when a pH indicator and an acid are previously contained in an absorptive material into which a liquid penetrates, and one end of the absorptive material is dipped in saliva, during a step when the saliva penetrates into the absorptive material, a buffer capacity functions against the acid previously contained in the absorptive material by the action of carbonic acid and a bicarbonate in the saliva, whereby the saliva continues to exhibit neutrality as in an oral cavity at the initial stage. However, when the saliva further penetrates into the absorptive material and continues to be exposed to the acid, the saliva loses the buffer capacity, so that it can no longer exhibit the neutrality. Utilizing this matter, when one having a predetermined shape is prepared as the absorptive material in which a pH indicator and an acid have been previously contained, and an amount of saliva having penetrated into this absorptive material and an amount of saliva having changed the color to be exhibited by the pH indicator by the penetrated saliva are measured from a distance where the color to be exhibited by the pH indicator has changed by the penetrated saliva from a predetermined place of the absorptive material and a distance where the saliva has penetrated from a predetermined place of the absorptive material, the buffer capacity of the individual saliva can be examined simply without being influenced by an amount of saliva and preciously without being influenced by the subjectivity of an examiner. Thus, the present invention has been completed.
Specifically, the invention relates to an examination method of buffer capacity of saliva comprising dipping an end portion of an absorptive material in a predetermined shape, containing a pH indicator at least having one or more color transition range of pH 4.0 to 7.0 and an acid, in saliva to allow the saliva to penetrate into the absorptive material, and examining a buffer capacity of the saliva from a distance where a color to be exhibited by the pH indicator has changed by the penetrated saliva from a predetermined place of the absorptive material and a distance where the saliva has penetrated from a predetermined place of the absorptive material; and to an examination instrument of buffer capacity of saliva comprising an absorptive material in a predetermined shape, containing a pH indicator at least having one or more color transition range of pH 4.0 to 7.0 and an acid.
Further, it has been found that the absorptive material is preferably an absorptive material having a property such that, when the absorptive material with a constant lateral cross-sectional area is made to stand upright to a water surface and its end portion of 10 mm is dipped in water, a penetration distance of water is 10 to 200 mm under the conditions at a temperature of 23xc2x0 C. and at a humidity of 50% for 5 minutes; and that the acid contained in the absorptive material preferably has a normality of 0.005 to 5.0 N.